An epoxy resin forms a three-dimensional crosslinked structure by the reaction between an epoxy group in the epoxy resin and a curing agent, and is applied for various purposes such as electrical and adhesion purposes, including coating materials, because of its excellent physical, chemical and electrical properties. The epoxy resin typified by a bisphenol A type epoxy resin has a secondary alcohol structure composed of epihalohydrin and an aromatic dihydroxy compound, or a diglycidyl compound and an aromatic dihydroxy compound in a main chain, and is excellent in hydrophobicity excluding a side chain hydroxy group in the secondary alcohol structure. The side chain hydroxy group in the secondary alcohol structure has hydrophilicity but is not necessarily excellent in hydrophilicity. Therefore, the epoxy resin does not form a stable polymer micelle in water and hardly exhibits a function such as encapsulization peculiar to the polymer micelle.
For example, the epoxy resin can be water-solublized by neutralizing a semiesterified modified epoxy resin, which is obtained by reacting a hydroxy group in a side chain with an acid anhydride, with a base (see, for example, Japanese Unexamined Patent Application, First Publication No. Hei 5-70558), or neutralizing a tertiary amino group-modified epoxy resin, which is obtained by reacting a glycidyl group in an epoxy resin with a secondary amine, with an acid. However, these water-solubilized epoxy resin also do not form a stable polymer micelle in water and hardly exhibit a function such as encapsulization peculiar to the polymer micelle.